The invention is directed to the removal of gum and chlorophyll-type compounds from vegetable oils from seeds, especially frost damaged seeds which have large amounts of chlorophyll. More particularly, a single-step acid degumming/decolorizing process is provided using a mixture of aqueous sulfuric and phosphoric acids. The purified oil has less than about 5 ppm chlorophyll-type compounds, less than about 50 ppm phosphorus and less than about 1.0 weight percent free fatty acids.
An early frost will damage vegetable seeds, such as canola seeds and soybeans. As a result of the frost damage, the seeds will have increased levels of chlorophyll. The frost damaged seeds typically have chlorophyll levels of about 30 ppm to about 80 ppm and greater. It is even possible to have chlorophyll levels of about 100 ppm or more along with about 1 to about 3 weight percent gum in the oil.
Specifications for Type 1 degummed canola oil allow up to only 30 ppm of chlorophyll. Current commercial processes for acid degumming of the extracted oil are not able to achieve this low level when using frost damaged seeds, which are classified as Type 2 and 3, as feedstock.
The standard commercial process for removal of chlorophyll includes acid activated clay bleaching. This process, however, is not effective for purifying oil extracted from frost damaged seeds because of the large amounts of clay that are required to produce bleached canola oil having less than 30 ppm of chlorophyll-type compounds. The large volume of clay needed makes treatment of frost damaged seeds very expensive. Moreover, the volume of clay required to decolorize may be so excessive, the process becomes commercially impractical. Thus, it is either not possible to produce purified, degummed oil to meet specifications when using frost damaged seeds as feedstock, or it is very cost prohibitive.
There is a need for a cost-effective process for treating oil extracted from vegetable seeds, especially frost damaged seeds, to provide a purified, degummed oil having a maximum of 30 ppm chlorophyll-type compounds.
The invention provides a method for removing gum and chlorophyll-type compounds from oil extracted from seeds, including canola seeds and soybeans, especially frost damaged seeds, to provide a purified, degummed oil. The degummed oil will have less than about 5 ppm chlorophyll-type compounds, less than about 50 ppm phosphorus and less than about 1.0 weight percent free fatty acids.
In a very important aspect of the invention, crude non-degummed vegetable oil, such as canola or soybean oil, containing chlorophyll-type compounds and gum is mixed with a mixture of aqueous sulfuric and phosphoric acid in a single-step acid degumming/ decolorizing purification process. The process does not require degummed oil, but rather is effective for the simultaneous removal of gum and chlorophyll-type compounds. The aqueous acids and water from the aqueous acids are in a ratio and in an amount which, when added to the oil, provides an acid/oil/water blend having a pH in the range of from about 1.5 to about 5 and which is effective for precipitating the gums and chlorophyll-type compounds from the vegetable oil. The precipitates are removed from the vegetable oil via centrifugation or filtration. Thereafter, the initially degummed oil is washed with water (pH of about 7-9) in an amount effective for raising the pH to at least from about 6 to about 7.5. In general, after acid degumming and decolorization, the initially degummed oil is washed with water in an amount of from about 10 weight percent to effectively remove most of the remaining gums from the decolorized, degummed oil and remove acids from the degummed oil, hence raising the pH of the oil to from about 6 to about 7.5. Only small amounts, if any, of chlorophyll are expected to be removed by water washing. The degummed/decolorized oil has less than about 5 ppm chlorophyll, less than about 50 ppm phosphorus and less than about 1.0 weight percent free fatty acids.
In another important aspect, the process proceeds without regard for lowering the moisture level in the crude vegetable oil prior to mixing with the acids or with the addition of water to effectively remove most of the gums. The moisture content of the oil may be up to about 0.5 weight percent. If the moisture content of the oil is greater than about 0.5 weight percent, the amount of sulfuric acidic must be increased accordingly. After the acids (which have some water) are mixed with the oil, the total amount of moisture in the process is less than about 1.0 weight percent.
In yet another important aspect, the process of the invention can be used to remove chlorophyll from frost damaged canola seeds that have very high levels of chlorophyll-type compounds. For example, typical canola seeds have up to about 30 ppm chlorophyll. In comparison, frost damaged seeds accumulate chlorophyll, and oils made from such seeds will have chlorophyll in amounts in excess of 100 ppm. In a surprising aspect, it is possible to process in accordance with the invention the oil from frost damaged seeds to provide a purified, degummed oil having no more than about 5 ppm chlorophyll-type compounds.
In another important aspect, a caustic solution may be mixed with the degummed oil after water washing if it is desirable to remove additional amounts of free fatty acids as precipitated soapstock. The decolorized, degummed oil is mixed with a caustic to neutralize free fatty acids. In an important aspect, the caustic is sodium hydroxide having a concentration of from about 14 to about 20 Baume (Be).
The pH of the process is carefully controlled at between about 1.5 and about 5 during acid mixing. By controlling the pH, the chlorophyll-type compounds are maintained in a precipitated form to ensure maximum separation. If the pH increases above about 5, the chlorophyll-type compounds become water soluble. At a pH less than about 1.5, browning, or other color changes, of the oil will occur.
The chlorophyll-type compounds removed as by-product from the oil may be further processed to provide purified chlorophyll. The chlorophyll can be purified using any known purification process. The purified chlorophyll then can be used to provide color to food and other products.